Energizer Recharge Smart Charger charges 2 or 4 AA or AAA Ni-MH rechargeable batteries. 4 AA Ni-MH batteries are included. This charger comes with a battery fuel guage, and a countdown timer that shows how long until batteries are charged. When a non-chargeable or bad battery is inserted, an alert detects and shuts off charging. This Energy Star certified charger protects your rechargeable batteries, by charging at a safe, steady rate which improves the long-term health of Ni-MH batteries.